The present invention relates to a lactate oxidase useful as an enzyme for a reaction which is represented by "L-lactate+oxygen.fwdarw.pyruvic acid+hydrogen peroxide". The lactate oxidase is an enzyme useful for a reaction to generate pyruvic acid and hydrogen peroxide from L-lactate and oxygen. Such lactate oxidase is extremely useful to measure a concentration of a lactic acid in a body fluid such as blood, It has been known in the art, to which the present invention pertains, that the lactate oxidase is present in bacteria which are classified into Pediococcus genus, Streptococcus genus, and Aerococcus genus. This is disclosed in the Japanese Laid-open Patent Applications Nos. 58-4557 and 2-177886 as well as in the Japanese Patent Publication No. 59-10190.
It was confirmed that a lactate oxidase obtained from Streptococcus shows a relatively low thermal stability. At a temperature above 34.degree. C., the biological activity of this lactate oxidase is rapidly reduced. This is disclosed in the Japanese Patent Application No. 58-4557.
It was also confirmed that another lactate oxidase obtained from Aerococcus also shows a relatively low thermal stability. If this lactate oxidase is subjected to a heat treatment at a temperature of 65.degree. C. for ten minutes, the biological activity is reduced by 50% or more. This is disclosed in the Japanese Patent Application No. 59-10190.